We examine the spheroid growth and star formation quenching experienced by galaxies since z~3 by studying the evolutionwith redshift of the quiescent and spheroid-dominated fractions of galaxies from the CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) andGAMA(Galaxy and Mass Assembly) surveys. We compare the observed fractions with predictions from a semi-analytic model which includes prescriptions for bulge growth and AGN feedback due to mergers and disc instabilities. We facilitate direct morphological comparison by converting our model bulge-to-total stellar mass ratios to Śersic indices. We then subdivide our population into the four quadrants of the specific star formation rate-Sérsic index plane and study the build-up of each of these subpopulations. We find that the fraction of star-forming discs declines steadily, while the fraction of quiescent spheroids builds up over cosmic time. The fractions of star-forming spheroids and quiescent discs are both nonnegligible, and stay nearly constant over the period we have studied. Our model is qualitatively successful at reproducing the evolution of the two 'main' populations (star-forming discs and quiescent spheroids), and approximately reproduces the relative fractions of all four types, but predicts a stronger decline in star-forming spheroids, and increase in quiescent discs, than is seen in the observations. A model with an additional channel for bulge growth via disc instabilities agrees better overall with the observations than a model in which bulges can grow only through mergers. We also examine the relative importance of these different physical drivers of transformation (major and minor mergers and disc instabilities).
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- Galaxies: bulges
- Galaxies: evolution
- Galaxies: interactions: galaxies: star formation